On Sunday, Sen. Marco Rubio (R-Fla.) was asked whether he’s ready to be president. He answered: “I mean, I’ll be 43 this month, but the other thing that perhaps people don’t realize: I’ve served now in public office for the better part of 14 years. And most importantly, I think a president has to have a clear vision of where the country needs to go and clear ideas about how to get it there. And I think we’re very blessed in our party to have a number of people that fit that criteria.”

** FILE ** Departing U.S. President Ronald Reagan is seen shortly after he delivered his farewell address to the nation at the Oval Office in the White House, Washington, on January 12, 1989. Reagan died Saturday, June 5, 2004 at his home in California, according to a friend, who spoke on condition of anonymity. He was 93. (AP Photo/Ron Edmonds) Departing U.S. President Ronald Reagan is seen shortly after he delivered his farewell address to the nation at the Oval Office in the White House on Jan. 12, 1989.  (Ron Edmonds/Associated Press)

Certainly, by 2016 Rubio will have had more legislative experience than President Obama did when he ran for president in 2008. But is that and a “clear vision of where the country needs to go” enough to prepare one for the presidency? In the last 5 1/2 years, we’ve gotten a look at what happens when a lightly credentialed president with zero executive experience winds up in the Oval Office. The biggest debacles — the Obamacare rollout, foreign policy flubs, the failure to reach a grand bargain — were in large part leadership and executive failures. Think about it: Obama’s administration was unprepared to initiate his most important domestic initiative (Obamacare) and he didn’t know about it (presumably).

In one sense, nothing really prepares on for the presidency. George W. Bush had been governor and had seen his father’s White House up front, but nothing really prepared him for the Sept. 11, 2001, terrorist attacks. It was a once-in-a-generation event. Unless one has been a chief executive, a military commander, a diplomat and a public policy expert, the White House is going to challenge any mortal, even one who has been vice president or held a key cabinet position. Not only is the broad array of issues beyond the expertise of most everyone who runs, but the toughest decisions on issues that divide even the president’s closest advisers wind up on the president’s desk.

In figuring out who is prepared to lead the Free World, there are a few clues about presidential preparation that can aid voters:

First, knowing what you want to do is not preparation; it is motivation for the presidency. Everyone running for president wants to do something. The question is whether that vision is sound and whether he or she can accomplish it. And knowing something about what you’re talking about sure helps. Seriously, did Obama really understand the Middle East or did he have an academic’s conception that came nowhere close to reality? Conversely, Ronald Reagan knew a thing or two about communism since he had spent decades studying it, reading about it and speaking about it.

Second, unless the candidate is the next Abraham Lincoln (or even Harry Truman), it is generally best to have executive experience of some type. That may be leading a state or an army, but knowing how to create consensus, assure buy-in and execute a game plan is the essence of presidential leadership. If you have never done this, the presidency is a very tough place to get on-the-job training.

Third, a lot of being president is about conflict resolution. You settle fights between State and Defense departments, between the House and Senate, between Congress and the executive branch, between foreign powers and between groups of constituents. There is a skill in reaching resolution, seeing where disputes are resolvable and where they are not. Unless a new president has some unique, inherent talent in this regard, if he’s not practiced in this area he is likely to be overwhelmed by conflicting demands and handicapped in deal-making. A loner who doesn’t enjoy the hurly-burly of politics and can’t figure out how to work with adversaries and allies alike is going to be a disaster.

And finally, there is character. Public character can be separated from private morality, to be certain; but gross character flaws (impulsiveness, hubris, dishonesty) often show up in public and private settings. For a president, character — as Obama has learned in his second term — is critical, for once the public no longer believes or trusts you, it is hard to accomplish much of anything. Once adversaries doubt your commitments, you will be challenged at every turn. Perseverance, loyalty and some self-awareness are critical. The president has to withstand adversity, naysayers and critics, and a president used to only cheers will be overwhelmed. As for self-awareness, humility in a president may be too much to ask, but the ability to not take the sycophantic praise too seriously and to insist upon hearing unpleasant, bad news is often the difference between catastrophe and success. Likewise, a thin-skinned and/or paranoid personality is a recipe for presidential disaster.

In short, if the candidate has a solid understanding of the issues confronting the president (grounded in reality, we would hope), some challenging executive experience, conflict resolution skills and solid public character, then I think it is fair to say he or she is prepared to be president. Rubio is right that lots of Republican presidential aspirants have a vision, but not all of them have a vision that is wise and attainable, and certainly many lack one or more of these four qualities. Very few have all of these qualities. You never really know how a president is going to turn out, but if a presidential aspirant is short on accurate knowledge, lacks executive skills, can’t work with others to reach consensus and lacks key aspects of public character, the country should run the other way. And, as in every modern primary race, there will be a few of those clunkers in 2016. Republicans should shrewdly assess their choices.